1. Field of the Invention
The present invention relates to a system for the production of semiconductors or the like, and more particularly to a method and apparatus for carrying a variety of products and for controlling the flow of articles to be processed by the structure of carriage equipment. The invention further relates to the structure of the processing apparatus and the control thereof in order to realize a carriage system suitable for a production line for a variety of flexible products.
2. Description of the Related Art
In the past, a production line in a semiconductor manufacturing factory has been divided into a working area which requires a clean atmosphere in which processing apparatuses for processing, carrying and storing wafers are installed, and a preservation area, which has less stringent requirements for cleanliness, in which accessory equipment and utilities are installed, as disclosed in Japanese Patent Application Laid-Open No. 19635/1981 and the like. Therefore, there has been employed a construction called a bay system in which working areas and preservation areas are alternately provided to the left and right of a central passage in order to effectively arrange the aforementioned apparatuses. The arrangement of the processing apparatuses relies upon a so-called job shop system in which the same kind of processing apparatuses are arranged in one bay in the bay system.
The carriage of wafers has been carried out by putting wafers into a cassette (sometimes called a carrier) and receiving the cassette into a cassette case, as shown in Japanese Patent Application Laid-Open No. 29923/1988.
In the bay system, the carriage of wafers between the processing apparatuses consists of a carriage in the bay and a carriage between bays, with a stocker for receiving cassettes provided at an exit of the bay constituting a connection point therebetween. Namely, the carriage in the bay is to carry the cassette from the stocker for the cassette provided at the inlet of the bay, and the carriage between the bays is to carry the cassettes from the stocker for one bay to the stocker for another bay. Therefore, the carriage of wafers from one processing apparatus to the other has been generally carried out in the course of the carriage in the bay.fwdarw.stocker.fwdarw.carriage between the bays.fwdarw.stocker.fwdarw.carriage in the bay.
An example of a railless carriage is a carriage called an AGV (Automatic Guided Vehicle), which carries several cassettes loaded at a low speed. An example of a rail-carriage that carries several cassettes loaded thereon as shown in Japanese Patent Application Laid-Open No. 185336/1987.
The charging of a wafer into the processing apparatus has been carried out in a manner such that a self-propelled robot handles one cassette as disclosed in Japanese Patent Application Laid-Open No. 48038/1987. Namely, when wafers are processed, the self-propelled robot takes out a cassette from the stocker and travels to a position in front of the processing apparatus to deliver the cassette to a loader portion to charge a wafer into the apparatus. When all the wafers stored in the cassette have been processed, the self-propelled robot travels to a position in front of the processing apparatus to remove the cassette from the loader portion and travels to the stocker to store cassettes in the stocker.
For the purpose of cleanliness, generally, the preservation area in which the accessory equipment and utilities are installed and the working area in which the processing apparatus is installed are alternately provided to left and right of the central passage. As a further example, the accessory equipment and utilities are provided on the first floor and the processing apparatus is installed on the second floor so that the processing apparatus can be laid out freely. Alternatively, there has been proposed a system for providing a partial clean room as disclosed in Japanese Patent Application Laid-Open No. 143623/1985. This system is done by setting a box containing a cassette to an interface provided on the processing apparatus in advance of when a wafer is charged into the processing apparatus in order to keep the clean area space to a minimum. In this manner, the wafer is delivered in a clean state, cutting off the atmosphere from the outside.
However, the conventional production systems possess the following problems.
First, the semiconductor process has many process steps, and many of the same steps are repeated. Therefore, in the conventional bay system, the carriage course between the bays becomes complicated and slow. In addition, since the state of the apparatus in pre-process and of that in post-process is known, the apparatuses are difficult to synchronize. Therefore, the quantity of inventory increases in each bay, as a consequence of which the term of work becomes extended. Even if the production line is of the flow shop system variety, the process flow differs by product, and therefore, it cannot cope with the production of a variety of products. In addition, since the process often changes and products are frequently switched, it is contemplated that the lay-out has to be frequently changed.
Furthermore, in charging wafers into the processing apparatus, wafers have to be charged into the processing apparatus arranged within one bay by one and the same self-propelled robot. However, in the current apparatus for manufacturing semiconductors, the height and depth of position at which a cassette is charged and the direction of cassette travel differ for each processing apparatus, only the processing apparatus in which the self-propelled robot traveling within the bay can charge the cassette is installed in one bay, and selection and lay-out of the processing apparatus are subjected to many restrictions. Moreover, where a processing apparatus is newly introduced, there is a possibility that the apparatus cannot be used in terms of restriction of the self-propelled robot.
Furthermore, since the processing apparatus is distanced form the stocker for storing cassettes, it takes time to some extent to charge a cassette into the processing apparatus. Since one self-propelled robot is provided for several processing apparatuses, cassettes cannot be simultaneously charged into a plurality of processing apparatuses. The availability factor of the processing apparatuses is thus suppressed to a lower level due to these factors.
With respect to a bay system which is maintained at high cleanliness, the space for requiring cleanliness is large, and it requires a huge investment to maintain high cleanliness, thus increasing operating costs. In addition, since the wafers are not separated from an operator in terms of atmosphere, it is very difficult to maintain the interior of a clean room at high cleanliness.
On the other hand, in the system for setting the cassette box to the interface, wafers are received into the cassette and closed, and therefore it is difficult to handle them one by one. In addition, since the atmosphere surrounding the wafer is still, once dust occurs, it cannot be removed and the dust may adhere to the wafers.
In semiconductors, a variety of products are required in a small quantity for each product as represented by ASIC. The trend is that production demand of a variety of products in small quantities will likely increase in the future. Therefore, the lot size may become so small that only ten sheets or so are received in a cassette having a capacity for 25 sheets. Also, the lot size differs with the products. Therefore, the number of cassettes which have to be carried increases despite the same production quantity as for the prior art, thus requiring higher carriage capability than in the prior art.
Moreover, there is a growing need for the diameter of a semiconductor wafer to increase from 4 inches to five inches, and to six inches as compared with the prior art. There is further a possibility that the diameter of a wafer will increase to eight inches in the future. Therefore, the carriage of wafers by cassette unit will become increasingly complex.
Furthermore, current processing apparatuses utilize single-wafer processing which processes wafers sheet by sheet.
As described above, it is expected that the trend of the production of a variety of products in a small quantity, the increasing diameter of wafers and the employment of apparatus for processing a single wafer will continue. Under these circumstances, it is very difficult to collectively manage about 25 wafers by cassette unit in the light of the optimum lot size and the weight of a cassette for the production of a variety of products in small quantities.